WO 2005/006538 A1 is based on a small electric device having an electric motor for producing an oscillating movement. Two drive components are provided, one of which is connected by means of at least one elastic element to a flexible part and can be activated; it can instigate an oscillating movement by means of a magnetic field of an inductor. The two drive components are connected to each other by means of an additional element and are designed so that they mutually drive each other and are arranged in the small electric device for executing oscillating movements in phase opposition to each other.
Electric motors are known that can generate a rotatory and translatory oscillating movement and which are used, for example, for electric toothbrushes. An electric motor like the one described in WO 2005/062445, has two oscillatory motor components and a magnet arrangement having several permanent magnets. An inductor is provided to produce a magnetic field. Interacting with the magnet arrangement, this magnetic field acts to generate a force to activate a translatory oscillating movement of one of the oscillatory components. The interaction of the magnetic field produced with the inductor and the magnet arrangement also generates torque for activating a rotatory oscillating movement of a second oscillatory motor component. With such an arrangement, both a translatory and a rotatory oscillating movement can be generated; no drive is required.
According to EP 0 850 027 B1, an electromotive drive unit is provided in a casing that, on the one hand, transfers a rotating movement with the help of a drive to a shaft, which movement can be converted, for example, into a rotating movement of a bristle head of the toothbrush. A second component of the electromotive drive unit is connected to the output of the electric motor eccentrically and thus activates a translatory oscillating movement of an oscillating crank around an axis at right angles to the motor axis. The oscillating crank helps to make this pivoting movement and the shaft led into it, which helps transfer the rotatory oscillating movement.
WO 2005/048437 describes a drive unit for producing an oscillating movement, for example, for producing a rotation oscillation of the bristle head of an electric toothbrush or of an electric shaving apparatus. A non-rotation-symmetric rotor moves within a stator that has an inductor and a first and a second magnet arrangement. The rotor has a first and a second radial extension, wherein the magnet arrangements relative to the radial extensions of the rotor allow for a paired allocation between the magnet arrangements and the radial extensions. At the same time, the arrangement is selected in such a way that the magnetic interaction between the magnet arrangement and the radial extension of each pair is greater than the magnetic interaction between the magnet arrangement and the radial extension of two different pairs. This makes it possible to design a rotor with a lower mass and a lower moment of inertia. The rotor is coupled with the stator by means of a righting interaction provided by an elastic element and thus forms an oscillatory system. A periodic pole reversal of the current flow into the inductors produces in this case an oscillating rotation of the rotor. Moreover, the respective rotation in the direction of the “off” position is facilitated by the righting moment produced by the elastic element. As an additional spring, the magnetic righting moment that is exercised on the rotor by the magnets of a magnet arrangement is taken into account. As an elastic element for the righting interaction, embodiments describe a torsion bar, a coil spring or a spiral spring that helps to couple the rotor with the stator. The resonance frequency depends on the spring/mass system formed by the rotor and the elastic element, for example, the torsion bar.